The plants east and south of this small plateau can be destroyed. That will give you access to the stuff on top.

This secret is hard to get to; once the wires at 4 are smashed, rush out on top of the sinking door and run towards the other end. Flip around and do a rocket jump. That might be sufficient to get you in.

a-b Jump up to the small pillar at a using the rocket launcher. That will teleport you to b.